1. Field of the Invention
The present invention relates to a novel regulatory element which confers microspore-specificity to gene expression. In particular, this invention is directed to a microspore-specific regulatory element of the Brassica napus Bnm1 gene, and to using such a regulatory element to produce transgenic, male-sterile plants. This invention also is directed to a method for restoring male fertility in the progeny of male-sterile plants. Moreover, the present invention relates to the use of a microspore-specific regulatory element to protect against viral and insect pests.
2. Background
Control of pollen fertility is essential in hybrid crop production. Traditional methods for regulating pollen fertility include manual emasculation of plants to be used as the female parent and application of chemical compositions. According to the latter method, hybrid seeds are produced by the cross fertilization of chemically-treated female plants with pollen from non-treated plants. Both approaches, however, are labor-intensive. Moreover, it is preferable to avoid the introduction of toxic chemicals into the environment.
Another approach to the control of fertility is based upon the use of a cytoplasmic gene(s) for male sterility. The problem with this approach is that the expression of certain cytoplasmic male sterility genes is accompanied by an increased susceptibility to fungal pathogens. For example, the extensive use of the cmsT cytotype in maize led to an epiphytic outbreak of Southern Corn Leaf Blight in the early 1970's. Although additional cytoplasmic male sterility cytotypes have become available, their use has not become widespread due to the concern over possible susceptibility to pathogens.
The ability to produce hybrid lines has particular economic importance for oil seed crops. For example, Brassica napus F.sub.1 hybrid lines typically produce yields that are greater than 20 to 70%, compared with established lines. Thompson, Adv. Appl. Biol. 7: 1 (1983); Johnston, Euphytica 20: 81 (1971). The most economic and flexible approach to controlling fertility in Brassica utilizes a self-incompatibility system that is naturally present in Brassica species. Gowers, Euphytica 24: 537 (1975). However, the self-incompatibility system is not reliably effective under certain environmental conditions, such as elevated temperatures.
A need therefore exists for a method to control pollen production without reliance on naturally occurring male sterility or self-incompatibility genes or, the traditional manual and chemical methods.